The present invention relates generally to optical encoding and decoding arranegements, and more particularly, to optical encoding and decoding arrangements which employ phase conjugation principles and four-wave mixing in particular.
Pulse encoding and decoding systems are commonly known in the electronics, microwave and optical arts. Such systems may be employed in radars, communications equipment which require pulse compression or cryptographic encoding of signals, or other similar systems. Although pulse encoding and decoding systems are well-known in the electronics and microwave arts, applications of these techniques for use in the optical frequency range has been quite difficult, typically due to the requirements of high precision in the optical components.
For instance, the tapped delay line matched filter, which is well-known in the microwave art, has been proposed for use in optical encoding/decoding applications. However, in order to achieve a useful matched filter, outputs from each segment of the filter must add coherently, and thus the segments must be well-controlled in path length to a precision of .lambda./10 or better at the the optical wavelength of interest. In addition, drifts in the effective path lengths induced by temperature or aging effects seriously degrades the use of this device at optical frequencies.
Thus, it would be an improvement in the optical filtering and signal processing arts to provide an optical encoding/decoding system for use at optical frequencies which does not require high-precision tolerances in the optical components as do prior art systems.